A liquid crystal display (LCD) device includes two substrates facing and spaced apart from each other and a liquid crystal layer between the two substrates, and uses the optical anisotropy and polarization properties of liquid crystal molecules of the liquid crystal layer to produce an image. The liquid crystal molecules have long and thin shapes, and because of the optical anisotropy property, the polarization of light varies with the alignment direction of the liquid crystal molecules. Accordingly, the LCD device displays an image by controlling the alignment of the liquid crystal molecules as well as the transmittance of light through the liquid crystal layer due to adjustment of the electric field applied to the liquid crystal layer. Among the various types of LCD devices, active matrix LCD (AM-LCD) devices that employ switching elements and pixel electrodes arranged in a matrix structure are the subject of significant research and development because of their high resolution and superior suitability for displaying moving images.
According to the property of liquid crystal molecules, the forming method of liquid crystal layer and the driving method, the LCD devices may be classified into a twisted nematic (TN) mode, a super twisted nematic (TN) mode, an optically compensated birefringence (OCB) mode, an in-plane switching (IPS) mode and a vertical alignment (VA) mode. Specifically, the VA mode LCD device using negative type liquid crystal molecules having a negative dielectric constant anisotropy and a vertical alignment layer includes a liquid crystal layer where a longer axis of the liquid crystal molecules is aligned perpendicular to an alignment layer. The VA mode LCD device has advantages in contrast ratio and viewing angle.
Although an LCD device having a relatively wide viewing angle is generally preferable, an LCD device having a relatively narrow viewing angle is requested for privacy in a certain circumstance such as an automatic teller machine (ATM).
Recently, an LCD device which is driven switchably between a wide viewing angle mode and a narrow viewing angle mode has been researched and developed. FIG. 1 is a cross-sectional view of a liquid crystal display device switchable between a wide viewing angle mode and a narrow viewing angle mode according to the related art. In FIG. 1, an LCD device 10 includes first and second liquid crystal cells 20 and 40. The first liquid crystal cell 20 is used as a main cell displaying images corresponding to a data signal, and the second liquid crystal cell 40 is used as a switching cell changing a drive mode by controlling a viewing angle according to user's selection.
The first liquid crystal cell 20 includes first and second substrates 22 and 24 facing and spaced apart from each other, a first liquid crystal layer 26 between the first and second substrates 22 and 24, and first and second polarizing plates 28 and 30 on outer surfaces of the first and second substrates 22 and 24, respectively. The second liquid crystal cell 40 includes third and fourth substrates 42 and 44 facing and spaced apart from each other, a second liquid crystal layer 46 between the third and fourth substrates 42 and 44, and third and fourth polarizing plates 48 and 50 on outer surfaces of the third and fourth substrates 42 and 44, respectively. After the first and second liquid crystal cells 20 and 40 are separately formed, the LCD device 10 is completed by attaching the first and second liquid crystal cells 20 and 40.
The LCD device 10 is driven in one of a wide viewing angle mode and a narrow viewing angle mode according to user's selection. When the LCD device 10 is driven in the wide viewing angle mode, light along any viewing angle is transmitted through the second liquid crystal cell 40. As a result, a wide viewing angle image displayed by the first liquid crystal cell 20 is transmitted through the second liquid crystal cell 40 and the LCD device 10 displays the wide viewing angle image. When the LCD device 10 is driven in the narrow viewing angle, light along a front viewing angle is transmitted through the second liquid crystal cell 40 and the second liquid crystal cell displays a white text in a black background along a right-left viewing angle. Accordingly, a wide viewing angle image displayed by the first liquid crystal cell 20 is transmitted through the second liquid crystal cell 40 along the front viewing angle and is disturbed by the white text along the right-left viewing angle. As a result, the LCD device 10 displays a narrow viewing angle image.
However, since the LCD device 10 further includes additional elements such as the third and fourth substrates 42 and 44, the second liquid crystal layer 46 and the third and fourth polarizing plates 48 and 50 as compared with a conventional LCD device, the LCD device 10 is enlarged in weight and volume including thickness. In addition, since light from a backlight unit (not shown) of the LCD device 10 passes through the additional elements, brightness of the LCD device 10 is reduced. Furthermore, misalignment of the attachment of the first and second liquid crystal cells 20 and 40 causes deterioration of the LCD device 10, and apparatus and process for the conventional LCD device can not be adapted to the attachment step. Moreover, since the second liquid crystal cell 40 as a switching cell has a passive matrix type, the LCD device 10 can not be driven in various narrow viewing angle modes.